Many large and medium size telecommunication battery plants supply power to switching equipment loads connected through plant load contactors. These contactors may be controlled by an external board or module outside of the plant controller. Other systems may have the load contactors directly controlled by an office plant controller. In each of these implementations, not is enough information is presently utilized to effectively control the load disconnect function. One of the main purposes of a load disconnect contactor is to remove the attached load from the power bus when the plant bus voltage is deemed to be at some hazardous level to some of the power equipment components (typically, a low voltage level). For example, at low voltage levels, the attached equipment may generate excessive current drains which may permanently damage the equipment. Present load disconnect designs exhibit a load contactor chattering problem, a situation where the load contactor rapidly turns on and off due to system conditions. Load chattering can lower the life of the contactor, create unnecessary noise, and disrupt or damage attached equipment.
Chattering contactors can be produced by a variety of different plant scenarios, one of them being a total AC failure or an AC phase failure. These types of power failures to the plant will cause the power equipment to run on batteries. The battery in a discharge mode of operation will eventually lower the plant bus voltage all the way down below a designated load disconnect threshold value. After reaching the threshold value, the load is disconnected. After the load is disconnected, the plant bus voltage increases to a value above the disconnect threshold value, which may be above a preset contactor reconnect value, provided one exists. This allows the controlling contactor device to place the load back onto the bus which immediately drags the bus voltage down below the disconnect value (since the backup batteries have already been drained of capacity), hence load contactor chattering occurs. There are other situations which may occur that can cause a rectifier or a number of rectifiers to fail or stop producing power. Under these circumstances and under certain load conditions, chattering contactors may also result.
In the past, one circuit pack or module was used to make the decision to disconnect or reconnect the load contactor. While this system is relatively reliable, the decision was made without the consideration of any additional plant status information which would allow for a more proficient decision.
Accordingly, what is needed in the art is a contactor controller containing a disconnect and reconnect feature which utilizes not only standard equipment information, but also other sources of plant-wide information.